Experimental charge-density analysis towards predictive materials science

The ongoing increase in the number of experimental charge-density studies can be related to both the technological advancements and the wide applicability of the method. Regarding materials science, the understanding of bonding features and their relation to the physical properties of materials can not only provide means to optimize such properties, but also to predict and design new materials with the desired ones. In this tutorial, we describe the steps for a charge-density analysis, emphasizing the most relevant features and briefly discussing the applications of the method.

Displacement parameters from density-functional theory and their validation in the experimental charge density of tartaric acid

Advanced theory matches advanced experiment: anisotropic displacement parameters for tartaric acid have been calculated in the quasi-harmonic approximation and determined experimentally based on a charge density study.

Analysis of charge density in nonaaquagadolinium(III) trifluoromethanesulfonate – insight into GdIII—OH2 bonding

The experimental charge-density distribution in [Gd(H2O)9](CF3SO3)3 has been analysed and compared with the theoretical density functional theory calculations. Although the Gd—OH2 bonds are mainly ionic, a covalent contribution is detectable when inspecting both the topological parameters of these bonds and the natural bond orbital results. This contribution originates from small electron transfer from the lone pairs of oxygen atoms to empty 5d and 6s spin orbitals of Gd3+.

Charge density studies of energetic material: RDX

Experimental charge density study has been carried out for Cyclotrimethylene-trinitramine (space group Pbca), an explosive material from a low temperature X-ray diffraction experiment. The electron density was modeled using the Hansen-Coppens multipole model and refined to R=0.032 for 6226 unique observed reflections. The electron density, laplacian and electrostatic potential distributions are reported and discussed, especially, the properties of the bond (3,-1) critical points, which are thought to play a key role in the decomposition of the molecule. From the bond topological analysis of all the bonds, it is observed that the N–N bond is the weakest. The dominating nature of the oxygen atoms was clearly well understood from isosurface electrostatic potential of isolated and symmetrically sitting molecules in the crystal.

Experimental charge density of grossular under pressure – a feasibility study

X-ray diffraction studies of crystals under pressure and quantitative experimental charge density analysis are among the most demanding types of crystallographic research. A successful feasibility study of the electron density in the mineral grossular under 1 GPa pressure conducted at the CRISTAL beamline at the SOLEIL synchrotron is presented in this work. A single crystal was placed in a diamond anvil cell, but owing to its special design (wide opening angle), short synchrotron wavelength and the high symmetry of the crystal, data with high completeness and high resolution were collected. This allowed refinement of a full multipole model of experimental electron distribution. Results are consistent with the benchmark measurement conducted without a diamond-anvil cell and also with the literature describing investigations of similar structures. Results of theoretical calculations of electron density distribution on the basis of dynamic structure factors mimic experimental findings very well. Such studies allow for laboratory simulations of processes which take place in the Earth's mantle.

Formate-mediated magnetic superexchange in the model hybrid perovskite [(CH3)2NH2]Cu(HCOO)3

The hybrid-perovskite [(CH3)2NH2]Cu(HCOO)3 shows antiferromagnetic and ferromagnetic interactions, as predicted by the GKA rules, proven applicable by experimental charge-density analysis.